The material properties marked as
"Type Float" ( see figure 1 ) have an extra animation feature, you can
control their "tweening".

Example, the property named "Ambient strength"

Say
we create 2 keys for "Ambient strength", the first one at frame 0 with a
value of 0% and the other at frame 100 with a value of 100%

For
frames 1 to 99, Daz Studio is in charge of computing the value of
"Ambient strength", a value somewhere in-between 0% and 100%.

The act of computing in-between values is called "interpolation" or "tweening".

By
default Daz Studio uses "Hermite" or "Splined" tweening to compute the
in-between values. What this means is, the value of "Ambient strength"
will slowly start increasing from frame 1 to 50, speeding up, then from
frame 50 to 99 it slows down until it reaches 100%

often,
you will want your values to ramp up from one key to the other at a
steady rate in our example, at frame 40 we would like to have "Ambient
Strength" at 40%, and we want it to be 90% at frame 90. This behaviour
is called "Linear " tweening

if
we want the value of "Ambient Strength" to remain at 0% from frames 0
to 99, then jump to 100% at frame 100, what we want is called "Constant
interpolation", sometimes called a staircase.

in
figure 3 you can see the cone's "Ambient Strength" animated with
"Constant" tweening"and the sphere's "Ambient Strength" animated with
"Linear" tweening"

figure 3. click on this image to see the animation

MatAnim
has a button to set the tweening for the key at the current frame (if
any ) and one to set the tweening for all existing keys. This works in
conjunction with the Linear/Constant/Splined checkboxes

if you
modify or create new keys, it's possible the tweening for those keys
will revert to "Splined" since that's the default behavior set by Daz
Studio. So setting the tweening may preferably be performed once all the
keys are laid out.